1. Field of the Invention
The present invention relates to a data compression system that is operative to compress time series data to produce a compression data (compression code), a data decompression system that is operative to expand (decompress) a compression data to produce an original data and a supervisory control system that has a function for remotely supervising and controlling an object unit.
The present invention also relates to a computer-readable storage medium capable of storing thereon a program code that causes a computer to execute a data compression process and a computer-readable storage medium capable of storing thereon a program code that causes a computer to execute a data decompression (expansion) process.
2. Description of the Prior Art
Generally, in cases where an object unit such as, a device, a system or the like, which requires maintenance services such as adjustment, supervision or maintenance is arranged remotely from a center (service center), it is proposed to provide a remote maintenance system capable of communicating various time series data through a network between the object unit and the center.
In the conventional remote maintenance system, time series data gained by the object unit are compressed to be communicated to the remote side (the center which is remotely arranged to the object unit).
As a conventional data compression system for compressing the time series data of the object unit to produce compressed data thereby transmitting the compressed data to the remote side of the center, there is well known the data compression system which is disclosed in Japanese Patent Application Laid-Open Publication No. 8-65768.
According to the disclosed data compression system, the time series data are compressed by performing polygonal approximation by using the peak positions of the pseudo two-stage differential values of the time series data so that the compressed data are transmitted to the remote side center, whereby the event retrieving is performed from the characteristics of the polygonal approximation data of the transmitted compressed data.
Furthermore, there is also well known the data compression system which is disclosed in Japanese Patent Application Laid-open Publication No. 11-122604.
According to the disclosed data compression system, the measured time series data of the mechanical system as the object unit are processed by the fast Fourier transform (FFT) so that data only including the peak frequency, and the amplitude and phase information thereof are transmitted to the remote side center, so that the transmitted compressed data are decompressed on the remote side center in the form in which the state of the vibration of the measured time series data can easily visually understood.
However, in each of the conventional data compression systems, from the viewpoint of the degree of decompression of original data when decompressing the compressed data, it is hard to ensure a sufficient accuracy of the decompression.
That is, according to the conventional data compression system disclosed in Japanese Patent Application Laid-Open Publication No. 8-65768, there is the possibility that the peak determining accuracy by the pseudo two-stage differential information necessary for the polygonal approximation is considerably damaged by the complexity of the behavior of the time series data or the inclusion of noise therein.
In addition, in the case where the time series data has oscillating response characteristics, there is the high possibility that the compression processing to the time series data damages the characteristic thereof, such as “oscillating”, or the like, and therefore, it is difficult to accurately supervisory and control the object unit and to provide a service based on a high-level judgment to the object unit with a practical communication load.
Furthermore, according to the conventional data compression system disclosed in Japanese Patent Application Laid-Open Publication No. 11-122604, because the waveform information on non-stationary behavior thereof , that is, on the time base, which is also the characteristic of the time series data, is lost in the FFT compressed data, it is difficult to accurately supervise and control the object unit.